Low PAPR full-diversity space-frequency codes for MIMO-OFDM systems

Use of precoding transforms such as Hadamard Transforms and Phase Alteration for Peak to Average Power Ratio (PAPR) reduction in OFDM systems are well known. In this paper we propose use of Inverse Discrete Fourier Transform (IDFT) and Hadamard transform as precoding transforms in MIMO-OFDM systems to achieve low peak to average power ratio (PAPR). We show that while our approach using IDFT does not disturb the diversity gains of the MIMO-OFDM systems (spatial, temporal and frequency diversity gains), it offers a better trade-off between PAPR reduction and ML decoding complexity compared to that of the Hadamard transform precoding. We study in detail the amount of PAPR reduction achieved for the following two recently proposed full-diversity Space-Frequency coded MIMO-OFDM systems using both the IDFT and the Hadamard transform: (i) W. Su. Z. Safar, M. Olfat, K. J. R. Liu (IEEE Trans. on Signal Processing, Nov. 2003), and (ii) W. Su, Z. Safar, K. J. R. Liu (IEEE Trans. on Information Theory, Jan. 2005).

BER analysis of space-time block codes from generalized complex orthogonal designs for M-PSK

In this paper, we present an analysis for the bit error rate (BER) performance of space-time block codes (STBC) from generalized complex orthogonal designs for M-PSK modulation. In STBCs from complex orthogonal designs (COD), the norms of the column vectors are the same (e.g., Alamouti code). However, in generalized COD (GCOD), the norms of the column vectors may not necessarily be the same (e.g., the rate-3/5 and rate-7/11 codes by Su and Xia in [1]). STBCs from GCOD are of interest because of the high rates that they can achieve (in [2], it has been shown that the maximum achievable rate for STBCs from GCOD is bounded by 4/5). While the BER performance of STBCs: from COD (e.g., Alamouti code) can be simply obtained from existing analytical expressions for receive diversity with the same diversity order by appropriately scaling the SNR, this can not be done for STBCs from GCOD (because of the unequal norms of the column vectors). Our contribution in this paper is that we derive analytical expressions for the BER performance of any STBC from GCOD. Our BER analysis for the GCOD captures the performance of STBCs from COD as special cases. We validate our results with two STBCs from GCOD reported by Su and Xia in [1], for 5 and 6 transmit antennas (G(5) and G(6) in [1]) with rates 7/11 and 3/5, respectively.

Storage and retrieval of individual genomes

A repetitive sequence collection is one where portions of a base sequence of length n are repeated many times with small variations, forming a collection of total length N. Examples of such collections are version control data and genome sequences of individuals, where the differences can be expressed by lists of basic edit operations. Flexible and efficient data analysis on a such typically huge collection is plausible using suffix trees. However, suffix tree occupies O(N log N) bits, which very soon inhibits in-memory analyses. Recent advances in full-text self-indexing reduce the space of suffix tree to O(N log σ) bits, where σ is the alphabet size. In practice, the space reduction is more than 10-fold, for example on suffix tree of Human Genome. However, this reduction factor remains constant when more sequences are added to the collection. We develop a new family of self-indexes suited for the repetitive sequence collection setting. Their expected space requirement depends only on the length n of the base sequence and the number s of variations in its repeated copies. That is, the space reduction factor is no longer constant, but depends on N / n. We believe the structures developed in this work will provide a fundamental basis for storage and retrieval of individual genomes as they become available due to rapid progress in the sequencing technologies.

BER analysis of space-time block codes from generalized complex orthogonal designs for M-PSK

In this paper, we present an analysis for the bit error rate (BER) performance of space-time block codes (STBC) from generalized complex orthogonal designs for M-PSK modulation. In STBCs from complex orthogonal designs (COD), the norms of the column vectors are the same (e.g., Alamouti code). However, in generalized COD (GCOD), the norms of the column vectors may not necessarily be the same (e.g., the rate-3/5 and rate-7/11 codes by Su and Xia in [1]). STBCs from GCOD are of interest because of the high rates that they can achieve (in [2], it has been shown that the maximum achievable rate for STBCs from GCOD is bounded by 4/5). While the BER performance of STBCs: from COD (e.g., Alamouti code) can be simply obtained from existing analytical expressions for receive diversity with the same diversity order by appropriately scaling the SNR, this can not be done for STBCs from GCOD (because of the unequal norms of the column vectors). Our contribution in this paper is that we derive analytical expressions for the BER performance of any STBC from GCOD. Our BER analysis for the GCOD captures the performance of STBCs from COD as special cases. We validate our results with two STBCs from GCOD reported by Su and Xia in [1], for 5 and 6 transmit antennas (G(5) and G(6) in [1]) with rates 7/11 and 3/5, respectively.

Rot bilong mipela

In my master's thesis I explore the political significance of logging in Papua New Guinea (PNG). In commercial logging the post-colonial state of PNG, its local communities, transnational companies and non-governmental organizations come interestingly together. The central research questions are what forms of political awareness and mobilization does commercial logging bring up in the small scale communities and how – if at all – does logging change the relationship between these communities and the state of PNG. The thesis is based on three months of ethnographic fieldwork conducted in 2007 in a village located in the East New Britain province of PNG. The village, inhabited mainly by the Mengen people, was an interesting case, because logging operations had been conducted in the area with the permission of the people, while on the other hand some villagers had formed a conservation association of their own. Parliamentary elections were also held in PNG during the time of my fieldwork. During my stay in the village I took part in the village life and conducted interviews. In addition to this, much of my material is based on informal discussions with people. On my way to and from the village I also interviewed several Papua New Guinean NGO-workers in the national and provincial capitals. In my thesis I show that environmental conservation in the village is part of a larger attempt to protect local autonomy, culture and the environment, i.e. it is a ”localistic” movement. Locals supporting conservation, as well as those supporting logging, take actively part in national parliamentary as well as local level politics. In my thesis I have attempted to unpack the notion of ”local” by examining internal power relations of the community and describing various lines of thought and opinions that base on local cultural values. Along with this, commercial logging seems also to elicit the role of the state in two-fold way in East New Britain. On the one hand, the government seeks to use logging roads built by logging companies as the basis of its own national infrastructure, even though the company roads are often of manifestably poor quality and short-lived. On the other hand, problems caused by logging, such as land disputes, create a need among local communities for the state and its services. Central themes in my thesis are the local values invested in the environment, as well as the ways in which the locals produce their environment both conceptually as well as physically. As subsistence farmers the locals depend economically on the condition of their environment. However, the value of the environment goes beyond economical questions. For example, the environment holds proof of the history of the community. Conversely, also the state and companies attempt to conceptualize, modify and administer the environment. This is done through processes such as mapping and road building, both crucial political questions in East New Britain. Here the anthropological discussion about space and place, as well as political geography are central. The diverse ways of conceptualizing the environment, as well as logging, cause often disputes about the ownership of land areas. Because of this I discuss local ways of holding the land communally, as well as PNG's land legislation and ways of dispute management. Land tenure and disputes are political questions that the locals have to deal with and in some cases these questions also create a need for the judiciary system of the state. The disputes affect also political activity, which I discuss at some length in my thesis as well. Interestingly, the locals, regardless of their political views and affiliations, establish transnational connections ranging from NGOs to government departments and multinational companies.

Space-charge limited conduction in doped polypyrrole devices

Doping dependent current-voltage (I-V) and capacitance-voltage (C-V) measurements were carried out on polypyrrole devices in metal-polymer-metal sandwich structure. Temperature dependent I-V measurements infer that space-charge limited conduction (SCLC) with exponential trap distribution is appropriate for the moderately doped samples, whereas trap-free SCLC is observed in lightly doped samples. Trap densities and energies are estimated, the effective mobility is calculated using the Poole-Frenkel model, and the mobility exhibits thermally activated behavior. Frequency dependent capacitance-voltage characteristics show a peak near zero bias voltage, which implies that these devices are symmetric with a negligible barrier height at the metal-polymer interface. Low frequency capacitance measurements have revealed a negative capacitance at higher voltages due to the processes associated with the injection and redistribution of space-charges. (C) 2010 American Institute of Physics.

Becoming an international man: Top manager masculinities in the making of a multinational corporation

Purpose We address gender and management in contemporary globalization by focusing on the ways in which male top managers in a multinational corporation (MNC) construct their identities in interviews with researchers. Design/methodology/approach Our qualitative analysis is based on interviews with virtually all top managers in the Nordic financial services company Nordea (53 men and two women). Findings We specify how becoming international induces a particular masculine identity for the top managers. In becoming international, however, their national identification persists. The unstability of the MNC as a political constellation leaves room for questioning the transnational identity offered. Originality/value Our findings suggest that in the global world of business, national identity can also be interpreted as something positive and productive, contrary to how it has been previously treated in feminist and men’s studies literature.

Language and the Circuits of Power in a Merging Multinational Corporation

We argue in this paper that corporate language policies have significant power implications that are easily overlooked. By drawing on previous work on power in organizations (Clegg, 1989), we examine the complex power implications of language policy decisions by looking at three levels of analysis: episodic social interaction, identity/subjectivity construction, and reconstruction of structures of domination. In our empirical analysis, we focus on the power implications of the choice of Swedish as the corporate language in the case of the recent banking sector merger between the Finnish Merita and the Swedish Nordbanken. Our findings show how language skills become empowering or disempowering resources in organizational communication, how these skills are associated with professional competence, and how this leads to the creation of new social networks. The case also illustrates how language skills are an essential element in the construction of international confrontation, lead to a construction of superiority and inferiority, and also reproduce post-colonial identities in the merging bank. Finally, we also point out how such policies ultimately lead to the reification of post-colonial and neo-colonial structures of domination in multinational corporations.

Language and the circuits of power in a merging multinational corporation

We argue in this paper that corporate language policies have significant power implications that are easily overlooked. By drawing on previous work on power in organizations (Clegg, 1989), we examine the complex power implications of language policy decisions by looking at three levels of analysis: episodic social interaction, identity/subjectivity construction, and reconstruction of structures of domination. In our empirical analysis, we focus on the power implications of the choice of Swedish as the corporate language in the case of the recent banking sector merger between the Finnish Merita and the Swedish Nordbanken. Our findings show how language skills become empowering or disempowering resources in organizational communication, how these skills are associated with professional competence, and how this leads to the creation of new social networks. The case also illustrates how language skills are an essential element in the construction of international confrontation, lead to a construction of superiority and inferiority, and also reproduce post-colonial identities in the merging bank. Finally, we also point out how such policies ultimately lead to the reification of post-colonial and neo-colonial structures of domination in multinational corporations.

Sensemaking in the Third Space - Essays on French-Finnish Bicultural Experiences in Organizations and Their Narratives (summary section only)

Research on cross-cultural and intercultural aspects in organizations has been traditionally conducted from an objectivist, functionalist perspective, with culture treated as an independent variable, and often the key explanatory factor. In order to do justice to the ontological relativity of the phenomena studied, more subjectivist research on intercultural interactions, and especially on their relationships with the dynamics of cultural identity construction, is needed. The present research seeks to address this gap by focusing on bicultural interactions in organizations, as they are experienced by the involved individuals. It is argued that such bicultural situations see the emergence of a space of hybridity, which is here called a ‘third space’, and which can be understood as providing ‘occasions for sensemaking’: it is this individual sensemaking that is of particular interest in the empirical narrative study. A first overall aim of the study is to reach an understanding of the dynamics of bicultural interactions in organizations; an understanding not only of the potential for learning and emancipatory sensemaking, but also of the possibility of conflict and alienatory ordering (this is mainly addressed in the theoretical essays 1 and 2). Further, a second overall aim of the study is to analyze the reflexive identity construction of four young French expatriates involved in such bicultural interactions in organizations in Finland, in order to examine the extent to which their expatriation experiences have allowed for an emancipatory opportunity in their cases (in essays 3 and 4). The primary theoretical contribution in this study lies in its new articulation of the dynamics of bicultural interactions in organizations. The ways in which the empirical material is analyzed bring about methodological contributions: since the expatriates’ accounts are bound to be some kind of construction, the analysis is made from angles that point to how the self-narratives construct reality. There are two such angles here: a ‘performative’ one and a ‘spatial’ one. The most important empirical contributions lie in the analysis of, on the one hand, the alternative uses that the young expatriates made of the notion of ‘national culture’ in their self-narratives, and, on the other hand, their ‘narrative practices of the third space’: their politics of escape or stabilization, their exploration of space or search for place, their emancipation from their origin or return to home as only horizon.

A non-orthogonal distributed space-time coded protocol - Part 1:Signal model and design criteria

In this two-part series of papers, a generalized non-orthogonal amplify and forward (GNAF) protocol which generalizes several known cooperative diversity protocols is proposed. Transmission in the GNAF protocol comprises of two phases - the broadcast phase and the cooperation phase. In the broadcast phase, the source broadcasts its information to the relays as well as the destination. In the cooperation phase, the source and the relays together transmit a space-time code in a distributed fashion. The GNAF protocol relaxes the constraints imposed by the protocol of Jing and Hassibi on the code structure. In Part-I of this paper, a code design criteria is obtained and it is shown that the GNAF protocol is delay efficient and coding gain efficient as well. Moreover GNAF protocol enables the use of sphere decoders at the destination with a non-exponential Maximum likelihood (ML) decoding complexity. In Part-II, several low decoding complexity code constructions are studied and a lower bound on the Diversity-Multiplexing Gain tradeoff of the GNAF protocol is obtained.

Switching frequency variation control in hysteresis PWM controller for IM drives using variable parabolic bands for current error space phasor

Variation of switching frequency over the entire operating speed range of an induction motor (M drive is the major problem associated with conventional two-level three-phase hysteresis controller as well as the space phasor based PWM hysteresis controller. This paper describes a simple hysteresis current controller for controlling the switching frequency variation in the two-level PWM inverter fed IM drives for various operating speeds. A novel concept of continuously variable hysteresis boundary of current error space phasor with the varying speed of the IM drive is proposed in the present work. The variable parabolic boundary for the current error space phasor is suggested for the first time in this paper for getting the switching frequency pattern with the hysteresis controller, similar to that of the constant switching frequency voltage-controlled space vector PWM (VC-SVPWM) based inverter fed IM drive. A generalized algorithm is also developed to determine parabolic boundary for controlling the switching frequency variation, for any IM load. Only the adjacent inverter voltage vectors forming a triangular sector, in which tip of the machine voltage vector ties, are switched to keep current error space vector within the parabolic boundary. The controller uses a self-adaptive sector identification logic, which provides smooth transition between the sectors and is capable of taldng the inverter up to six-step mode of operation, if demanded by drive system. The proposed scheme is simulated and experimentally verified on a 3.7 kW IM drive.

Distributed space-time codes with reduced decoding complexity

We address the problem of distributed space-time coding with reduced decoding complexity for wireless relay network. The transmission protocol follows a two-hop model wherein the source transmits a vector in the first hop and in the second hop the relays transmit a vector, which is a transformation of the received vector by a relay-specific unitary transformation. Design criteria is derived for this system model and codes are proposed that achieve full diversity. For a fixed number of relay nodes, the general system model considered in this paper admits code constructions with lower decoding complexity compared to codes based on some earlier system models.

Minimum-Decoding-Complexity, maximum-rate Space-Time Block Codes from Clifford algebras

It is well known that Alamouti code and, in general, Space-Time Block Codes (STBCs) from complex orthogonal designs (CODs) are single-symbol decodable/symbolby-symbol decodable (SSD) and are obtainable from unitary matrix representations of Clifford algebras. However, SSD codes are obtainable from designs that are not CODs. Recently, two such classes of SSD codes have been studied: (i) Coordinate Interleaved Orthogonal Designs (CIODs) and (ii) Minimum-Decoding-Complexity (MDC) STBCs from Quasi-ODs (QODs). In this paper, we obtain SSD codes with unitary weight matrices (but not CON) from matrix representations of Clifford algebras. Moreover, we derive an upper bound on the rate of SSD codes with unitary weight matrices and show that our codes meet this bound. Also, we present conditions on the signal sets which ensure full-diversity and give expressions for the coding gain.

Non-unitary-weight Space-Time Block Codes with Minimum Decoding Complexity

Space-Time Block Codes (STBCs) from Complex Orthogonal Designs (CODs) are single-symbol decodable/symbol-by-symbol decodable (SSD); however, SSD codes are obtainable from designs that are not CODs. Recently, two such classes of SSD codes have been studied: (i) Coordinate Interleaved Orthogonal Designs (CIODs) and (ii) Minimum-Decoding-Complexity (MDC) STBCs from Quasi-ODs (QODs). The class of CIODs have non-unitary weight matrices when written as a Linear Dispersion Code (LDC) proposed by Hassibi and Hochwald, whereas the other class of SSD codes including CODs have unitary weight matrices. In this paper, we construct a large class of SSD codes with nonunitary weight matrices. Also, we show that the class of CIODs is a special class of our construction.